Tobacco is the leading cause of preventable disease and death in the U.S. Although effective tobacco cessation medications exist, the impact of these medications is diminished by lack of adherence by the patient. Based on our team's expertise in the use of technology to improve evidence-based treatment of tobacco dependence and improving asthma medication adherence, we propose to develop and evaluate an interactive mobile health application (app) for helping smokers to properly use tobacco cessation medication. Over 85% of U.S. adults use a mobile phone, and 35% of those have apps on their phones. Although our project will focus on tobacco cessation medication, this app would have broad applicability beyond tobacco cessation treatment. Non-adherence to treatment for chronic conditions such as hypertension, hyperlipidemia, and diabetes has been associated with poor treatment outcomes, including increasing hospitalization rates and health care costs. The lessons learned in the proposed project could be applied to the development of mobile health apps for other types of medication. During Phase I, we will design, program and evaluate a prototype mobile health application for the Apple iPhone platform that will assist smokers who are prescribed Chantix(R) (vareniciline) for treatment of tobacco dependence to properly adhere to the medication regimen. The app will include modules aimed at addressing the most common reasons for medication non-adherence (e.g., forgetfulness, poor patient-provider communications, side effects, lack of belief in benefits of medication, etc.). Examples of modules include reminder systems (to prompt dosing and refills), direct linkage from the user to their prescribing physician or pharmacist (to discuss dosing schedule or side effects), and in-depth information about the effectiveness of varenicline and managing side effects. We will use 20 focus group participants to refine the application's interface, functions, and content. We will conduct usability testing with 10 participants to assist in improving the app's functionality and suitability. Finally, we will conduct a test of the app's feasibility and user acceptability with 20 participants. A within-subjects design will evaluate participants' reported usability and satisfaction with the product, users' reported adherence to varenicline, and their actual use of the mobile app. Adherence outcomes will be evaluated using a multi-modal approach, including rate of prescription refills, mobile app collected diary data, and self-report questionnaires. We will assess attitudes and user satisfaction via a mobile-web interface. Program use will be collected automatically via the mobile app. Participants will be assessed at baseline and 12-weeks post-enrollment. During Phase II, we will expand the application platform (e.g., Android and Blackberry) and content (e.g., other prescription tobacco cessation medications and over- the-counter nicotine replacement products), and evaluate the full application via a randomized trial. The final mobile health app will be marketed to smokers, health care providers, health plans (private and employer- based), pharmacy benefit managers, and tobacco quit lines through multiple channels, including the App Store, web-based tobacco cessation programs, Google Ads, social media sites, direct mail and phone.